A wheelbarrow is a device that is used to transport heavy loads by hand. A wheelbarrow consists of a tray mounted on a wheel and two legs with handles that extend to the rear. A wheelbarrow is moved by lifting its handles to raise the legs off the ground, balancing the loaded wheelbarrow on its wheel, and walking. A wheelbarrow is typically unloaded by dumping, i.e., lifting the handles to tip the tray into a vertical position where the load slides or pours out the sloped front end of the tray. A wheelbarrow is an example of a second-class lever in which the axle of the wheel forms the fulcrum and the handles form the effort arms.
Wheelbarrows are especially useful in moving loads across soft or uneven ground because the single wheel provides high maneuverability and also because the user can keep the load balanced by raising or lowering one or both of the handles. Wheelbarrows are also especially useful because of their ability to easily dump the load. However, as the weight of the load increases, it becomes more difficult to balance the wheelbarrow during movement and dumping. Dumping a heavy load is particularly difficult because the user must change from lifting the handles with an underhanded grip to pushing the handles with an overhanded grip while simultaneously balancing the wheelbarrow on a single wheel as the load rapidly shifts position. If the user loses balance of the wheelbarrow, the load is spilled at an undesired location and property damage and/or physical injury can occur.
Because of the difficulty in balancing a conventional wheelbarrow during dumping, many different modifications have been suggested. For example, Donze et al., U.S. Pat. No. 5,026,079, issued Jun. 25, 1991, discloses a wheelbarrow having multiple wheels and a horizontal abutment bar positioned in front of the wheels. The wheels are positioned in vertical alignment with the center of gravity of the tray so that the force required to lift the handles is minimized. The abutment bar is in horizontal alignment with the axles of the wheels and is in vertical alignment with the straight front edge of the tray. The abutment bar serves as a fulcrum for tipping the wheelbarrow and also enables the wheelbarrow to be balanced in a vertical storage position resting on the abutment bar and the straight front edge of the tray. The multiple wheels of the Donze et al. wheelbarrow provide improved stability during movement and dumping, but at the cost of decreased maneuverability and increased weight.
Broeske, U.S. Pat. No. 5,067,737, issued Nov. 26, 1991, discloses a wheelbarrow whose tray is in the form of a box having vertical side walls. The wheel is recessed into the bottom of the tray to provide a low center of gravity. However, the recessed wheel also reduces clearance, making the wheelbarrow unsuitable for use over uneven ground. When the Broeske wheelbarrow is tipped, the bottom front of the tray makes contact with the ground at an early point to form the fulcrum. However, the steep front of the tray requires the handles to be lifted well over vertical to empty the tray. Dumping rods are attached to the top front of the tray to raise the lid of the tray off the ground during dumping.
Several companies, including Kelley Manufacturing Company, sell a concrete cart having two large diameter wheels straddling the tray. When dumping, the cart tips forward on curved rocker arms. The concrete cart is not as maneuverable as a conventional wheelbarrow and has minimal ground clearance, making it suitable only for use on relatively flat and smooth ground.
Accordingly, a demand exists for a wheelbarrow that is as maneuverable as a conventional wheelbarrow, but is easier to dump and whose tray does not contact the ground during dumping.